Postpartum depression (PPD) is a significant public health issue for women and their families (5), yet research to date has focused almost exclusively on heterosexual married women (102). As a result, available research has not adequately studied the impact of sexual orientation on postpartum mental health. Sexual minority mothers may have distinct risk factors for PPD. In particular, minority stress and its manifestations (e.g., experiences of discrimination) have been associated with mental health outcomes in the general population of sexual minorities (37;39;48;56;75), although no studies have evaluated the impact of these variables on mental health in sexual minority women during the first postpartum year, a time of particular vulnerability to depression (132). Furthermore, while a very small body of literature (i.e., the PIs' research) has focused on mental health in sexual minority new mothers (46-52;100;101;103;111), these studies focus specifically on visible sexual minority women - that is, women who identify as lesbian or bisexual and who are partnered with other women. Preliminary pilot data indicate that invisible sexual minority women (i.e., women who have a history of sexual relationships with women in the past 5 years, but who are currently partnered with men) are at elevated risk for PPD during the transition to parenthood, compared to visible sexual minority women and heterosexual women. Our project aims to build upon this pilot work to examine several interrelated issues, which have important implications for future research and service delivery to both visible and invisible sexual minority women during the perinatal period. First, we aim to examine whether invisible sexual minority women (male-partnered women who have sexual histories including both men and women) have higher risk for depression at 6-8 weeks postpartum compared to either visible sexual minority women or sexual majority women (i.e., heterosexual women), after controlling for prenatal depression. Related to this first aim, we aim to explore whether anxiety symptoms, reports of positive mood, and patterns of health service utilization differ between invisible sexua minority, visible sexual minority, and sexual majority women at 6-8 weeks postpartum; whether invisible sexual minority women have different trajectories of depression, anxiety, or positive mood than other women during the first postpartum year; and, on a qualitative level, how invisible sexual minorities see their sexual/relationship histories, if at all, as influencing thei transition to parenthood and their current mental health. Second, we aim to examine whether minority stress processes (i.e., experiences of perceived discrimination, disclosure/concealment of sexual identity, and internalized homophobia), characteristics of minority identity, or LGBTQ-specific forms of social support (community and workplace support) mediate the relationship between minority status and mental health outcomes at 6-8 weeks postpartum, and whether minority stress processes, characteristics of minority identity, or LGBTQ-specific forms of social support mediate any relationship between minority status and patterns of health service utilization at 6-8 weeks postpartum. Related to this second aim, we aim to explore what barriers invisible sexual minority women report in seeking mental health or perinatal health services, and what suggestions they have for mental health or perinatal health providers, with regards to serving women with diverse sexual relationship histories and identities. This study will accomplish these aims through a multi-site, mixed-methods, longitudinal study of women who are recruited during pregnancy (20 visible sexual minority, 20 invisible sexual minority, and 100 heterosexual women). The findings will have implications for policy development and service delivery to visible and invisible sexual minority mothers.